This invention relates to forming substituted solid aromatic polymers.
Branched nitropolyphenylenes mixed with branched polyphenylenes are useful in preparing superior glass, graphite and carbon fiber composites. Such mixtures and composites are described in detail in U.S. Patent application Ser. No. 635,034 filed Nov. 25, 1975, now U.S. Pat. No. 3,974,121 incorporated herein by reference. Additionally, the nitropolyphenylenes can be reduced with such agents as tin to form aminopolyphenylenes which, in turn, can be polymerized further with polyfunctional acids or anhydrides or their respective chlorides, such as 4-trimellitoyl chloride anhydride, pyromellitic anhydride and the like, to form a polyphenylene amide-imide polymer. Such amide-imide polymers can be used in laminates. Sulfonated polyphenylenes can be used as cross-linking agents in forming glass composites and as ion exchange resins. These sulfonated polyphenylenes can be either water soluble or insoluble depending on the degree of sulfonation. Chloropolyphenylenes are useful as cross-linking agents in graphite and glass fiber composites. The branched polyphenylenes on which these substituted polyphenylenes are based are those novel branched polyphenylenes which possess increased solubility and thermal stability over a number average molecular weight range from about 1000 to over 10,000 which are described in U.S. Pat. Nos. 3,792,099, 3,855,332, 3,829,518 and 3,789,281 all incorporated by reference herein. Branched polyphenylenes have been found useful in high-temperature, corrosive conditions such as a binder for graphite powder in fuel cell plates, in ablative materials and in brake shoes. Such polyphenylenes also can be alkylated using boron trifluoride-formic acid catalysts to form oil additives or grease thickeners.
The nitropolyphenylenes described in Ser. No. 635,034 were produced by nitrating branched polyphenylene with a nitric acid-sulfuric acid mixture. Although such method produces suitable nitropolyphenylenes, the process has inherent disadvantages such as using highly corrosive acids which require a large volume of water to terminate the reaction and precipitate the product. Product filtration is often slow and requires extensive water washing and cumbersome spent acid disposal. Similarly, sulfonated polyphenylenes can be produced using sulfuric acid, however, such a method suffers from the same disadvantages as the above-described nitration procedure. There is a need for a convenient, easily controlled process which does not require extensive product work-up procedures. An especially preferred method would require neither solvent nor catalyst.
It is known to the art that aromatic systems can be nitrated with N.sub.2 O.sub.4 in solution in the presence or absence of various catalysts such as aluminum chloride, P.sub.2 O.sub.5, Lewis acid catalyst (e.g. BF.sub.3), p-chlorobenzoic acid, and palladium and thallium compounds. Benzene has been nitrated with N.sub.2 O.sub.4 induced by gamma radiation. Natural rubber possibly has been nitrated in benzene or dichlorobenzene solution using N.sub.2 O.sub.4. Biphenyl has been nitrated with excess liquid N.sub.2 O.sub.4 in the absence of ultraviolet light. Pyridine and toluene have been nitrated in the gaseous phase with N.sub.2 O.sub.4.